A hot-spot is a venue that offers WiFi access. Hot-spot wireless access is required by number of mobile devices, e.g., a laptop, Wi-Fi phone, or other device suitable to access the Internet. Of the estimated 150 million laptops, 14 million personal digital assistants (PDAs), and other emerging Wi-Fi devices sold per year for the last few years, most include the Wi-Fi feature. One of the critical tasks of hot-spot wireless access is to serve mobile devices crowded in a small area while the available wireless spectrum is limited.
Distributed Antenna System
To improve the throughput of hot-spot wireless access, distributed antenna system has been utilized. A Distributed Antenna System (DAS) is a network of spatially separated antennas connected to a common source via a transport medium that provides wireless service within a geographic area or structure.
FIG. 1 show an example of a distributed antenna system. The distributed antenna system partitions the transmitted power of antenna 101 among several antenna elements 102, separated in space so as to provide coverage for the mobile devices 103 over the same area as a single antenna 101 but with reduced total power and improved reliability. It is desired to improve performance of distributed antenna selection, by taking into the consideration the desired signal and interference strength as well as signal power allocation.
The Signal-to-Interference-plus-Noise Ratio (SINR) is an important metric of wireless communication link quality. SINR estimates have several important applications. These include optimizing the transmit power level for a target quality of service, assisting with handoff decisions and dynamically adapting the data rate for wireless Internet applications. Accurate SINR estimation provides for both a more efficient system and a higher user-perceived quality of service.
Signal power allocation is an intelligent selection of transmit power in a communication system to achieve good performance within the system. The notion of “good performance” can depend on context and may include optimizing metrics such as link data rate, network capacity, geographic coverage and range, and life of the network and network devices, and network capacity. Signal power allocation methods are used in many applications, including cellular networks.
Usually, a higher transmit power translates into a higher signal power at the receiver. Having a higher signal-to-noise ratio (SNR) at the receiver reduces the bit error rate of a digital communication link.
However, the higher transmit power leads to increase of power consumption in the transmitting device. This is of particular concern in mobile devices, where battery life is reduced correspondingly. Also, interference to other mobile device in the same frequency band is increased proportionally to the signal power. In cellular spread-spectrum systems such as CDMA, where the mobile devices share a single frequency and are only separated by different spreading codes, the number of mobile devices that a cell can support as well as the size of the cell is typically limited by the amount of interference present in the cell. The increased interference therefore results in decreased cell capacity and size. Even in FDMA systems such as GSM where each mobile device in a cell uses a different frequency, interference is still present between different cells and reduces the amount of frequency reuse the network can support.